The Syn-Rift Sequences:
Another Potential Play in Offshore Palawan
Paleocene to Eocene "Syn-Rift" sequences in offshore Northwest
Palawan consists mainly of marine deposits that filled rift
depocenters. A mid-Oligocene unconformity marking the initiation of
seafloor spreading in the South China Sea Basin separates the Syn-Rift
from the widespread platform carbonates of the Nido Limestone.
Buildups and folded fractured platform carbonates of the Nido
Limestone, and the directly overlying turbidites of the lower Pagasa
Formation have been the target of most exploration in NW Palawan.
Very few play concepts have been developed for the Syn-Rift
succession due to poor seismic data quality and the scarcity of
wells that have penetrated it. In horsts where most wells have been
drilled, most of the Syn-Rift successions, except for the topmost
few decameters, have low sandstone:mudrock ratios, giving a
perceived lack of reservoir quality sands.
presence of turbidites in Syn-Rift-equivalent units in Central
Palawan and new interpretation of 2D seismic data in the Syn-Rift
successions predict the presence of turbidite reservoirs in slope
and basinal paleoenvironments. Potential turbidite plays include
basin floor fans and leveed channels. The basin floor fan may reach
several km in one dimension and may be composed of more than one
lobe. It is convex-up and shows bidirectional downlap. The leveed
channel complex exhibits irregular and discontinuous reflections
with occasional channel patterns <1 km wide.
the main risks in a basin floor fan play is the lack of a local
condensed section above it to serve as seal. The main pitfall when
exploring for leveed channels is drilling a sand-poor channel fill.
The prospectivity of many of these deepwater plays is enhanced by
its lateral proximity to half-graben kitchen areas and favorable
burial history. Despite water depths from >1 to 21/2
km, the Syn-Rift interval can become a potentially significant
exploration target and warrants more detailed evaluation.